阅读说明：本技术 一种过热苯蒸气吹扫脱除液相法乙苯烷基化和转烷基化反应器催化剂内滞留液相苯的方法 (Method for removing liquid-phase benzene retained in catalyst of liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging ) 是由 张晶 徐志刚 和成刚 杨蓓玉 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种过热苯蒸气吹扫脱除液相法乙苯烷基化和转烷基化反应器催化剂内滞留液相苯的方法,以过热苯蒸气作为吹扫介质,可替代大部分液相法乙苯生产装置现用的蒸汽吹扫方法,有利于延长乙苯单元催化剂使用寿命,防止再生剂的选择性和转化率恶化；相比于热氮气吹扫脱除催化剂内液相苯的方法,该方法有利于减少循环氮气系统设备投资、降低氮气单程吹扫消耗,经济效益更为突出。(The invention discloses a method for removing liquid-phase benzene retained in a catalyst of a liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging, which takes superheated benzene vapor as a purging medium to replace most of existing steam purging methods of liquid-phase ethylbenzene production devices, is beneficial to prolonging the service life of an ethylbenzene unit catalyst and preventing the selectivity and the conversion rate of a regenerant from deteriorating; compared with the method for removing the liquid-phase benzene in the catalyst by hot nitrogen purging, the method is beneficial to reducing the equipment investment of a circulating nitrogen system and reducing the consumption of nitrogen once-through purging, and has more remarkable economic benefit.)

1. A method for removing liquid-phase benzene retained in a catalyst of a liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging is characterized by comprising the following main processes:

1) sending liquid-phase benzene separated by a reaction product separation system in a liquid-phase ethylbenzene production device into a benzene vaporizer to be vaporized into benzene vapor;

2) the benzene vapor forms superheated benzene vapor after passing through a benzene superheater and is sent into an alkylation reactor or a trans-alkylation reactor;

3) superheated benzene vapor purges liquid-phase benzene retained in an alkylation or transalkylation catalyst bed layer to be gasified, and the gasified gas-phase benzene enters a reaction product separation system to be condensed into liquid-phase benzene;

4) after liquid-phase benzene retained in the alkylation or transalkylation catalyst bed is removed, the benzene vapor feeding of the benzene superheater is switched to nitrogen, and the nitrogen is heated by the benzene superheater and then sweeps the gas-phase benzene retained in the alkylation or transalkylation catalyst bed.

2. The method for removing liquid phase benzene retained in catalyst of liquid phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging according to claim 1, wherein the superheated benzene vapor temperature for purging is 220-300 ℃.

3. The method for removing liquid phase benzene retained in a catalyst of a liquid phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging according to claim 1, wherein the superheated benzene vapor pressure for purging is 0.01-1.0 MPaG.

4. A superheated benzene vapor purge to remove liquid phase as claimed in claim 1The method for liquid-phase benzene retention in the catalyst of the ethylbenzene alkylation and transalkylation reactor is characterized in that the space velocity of superheated benzene vapor for purging is 2.01-60 h^-1。

Technical Field

The invention belongs to the field of petrochemical industry, and relates to a method for removing liquid-phase benzene retained in a catalyst of a liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging.

Background

Ethylbenzene is an important chemical raw material, and is mainly used as a raw material for producing styrene monomers, wherein styrene is a raw material of polystyrene and copolymers, and the ethylbenzene has a large market amount. At present, the production method of ethylbenzene mainly adopts the alkylation production method of benzene and ethylene. Benzene and ethylene are fed into an adsorption bed containing an adsorbent to remove impurities containing alkaline nitrogen, and then ethylbenzene is generated under the action of a Y-type molecular sieve, a beta-type molecular sieve or an MCM-type molecular sieve alkylation catalyst, and the generated ethylbenzene and ethylene can further undergo a multi-alkylation reaction to generate diethylbenzene and polyethylbenzene. After rectification and separation, the diethylbenzene and polyethylbenzene in the reaction product continuously react with benzene under the action of the transalkylation catalyst to obtain ethylbenzene, and then the ethylbenzene is returned to the separation system to be continuously separated.

The production process of ethylbenzene is divided into a pure ethylene process (raw material ethylene is polymerization-grade ethylene) and a dilute ethylene process (raw material is ethylene-containing dry gas, generally referred to as catalytic cracking dry gas) according to different ethylene sources; the method can be divided into a liquid phase method process and a gas phase method process according to different alkylation reaction phases, and the liquid phase method process has the advantages of better quality and lower energy consumption and material consumption compared with an ethylbenzene product prepared by the gas phase method process due to mild reaction conditions, and is an industrially preferred process route no matter a pure ethylene or dilute ethylene device. At present, the worldwide ethylbenzene productivity is about 4000 ten thousand tons, the Chinese productivity is about 1000 thousand tons, all newly-built pure ethylene ethylbenzene devices in the world adopt a liquid phase method process route, and the ethylbenzene produced by the liquid phase method ethylbenzene process route accounts for over 90 percent of the total ethylbenzene yield.

Through investigation, it was found that: the treatment procedures before the alkylation and transalkylation catalysts in each liquid-phase ethylbenzene production device are discharged are different, so that the difference of the using effect of the regenerated catalysts is large. The catalyst of part of users adopts a pretreatment procedure of removing liquid-phase and gas-phase benzene by steam purging before being discharged, and after detection, the loss of the specific surface area of the catalyst is up to 30 percent, which seriously influences the service life, the selectivity and the conversion rate of the regenerated catalyst. This also conforms to the theoretical basis that liquid water can cause the destruction of Y-type molecular sieve, beta-type molecular sieve or MCM molecular sieve catalyst framework aluminum. In addition, the water vapor is alkaline, and the alkaline substance reacts with the acidic catalytic active center of the Y-type molecular sieve, the beta-type molecular sieve or the MCM molecular sieve, so that the catalyst is deactivated in a non-renewable property. The world's leading ethylbenzene alkylation and transalkylation catalyst supplier UOP expressly prohibits the treatment of alkylation and transalkylation catalysts by steam purging.

The regeneration period of the alkylation and transalkylation catalyst by the liquid phase method is usually 3-4 years, the service life is 9-12 years, and the online coking quality of the catalyst is difficult to meet the requirements of catalyst suppliers, so most of the constructed ethylbenzene devices by the liquid phase method are not provided with an online coking system, but are replaced by an ex-situ regeneration method by professional catalyst regeneration manufacturers certified by the catalyst suppliers.

Catalyst regeneration, catalyst discharge and reactor maintenance in alkylation and transalkylation reactors all require operating procedures of removing organic matter in the catalyst bed and cooling to a temperature at which an operator can enter. The process must go through the process of removing liquid phase benzene and gas phase benzene in the catalyst bed, and the correct treatment process needs to be established to prevent the process from damaging the expensive catalyst.

Alkylation and transalkylation reactors are generally operated to achieve conditions that permit human access as follows:

(1) hot benzene replacement: replacing specific benzene heavy components contained in catalyst micropores in the reactor with hot benzene at 180-200 ℃, so as to reduce the difficulty of removing hydrocarbons;

(2) discharging: discharging liquid-phase benzene in the reactor and the catalyst, wherein experimental tests show that 80% of the liquid-phase benzene in the total amount of the catalyst is embedded in micropores and on the surface of the catalyst even after the liquid discharge of the reactor is finished;

(3) the pressure is reduced to 0.05 MPaG: after the liquid-phase benzene is discharged, the pressure in the reactor can be maintained at 1.0MPaG, 48 percent of the liquid-phase benzene contained in the micropores of the catalyst can be continuously evaporated into gas through adiabatic flash evaporation, and flash evaporation heat is provided by cooling the catalyst and the liquid-phase benzene;

(4) superheated steam replacement or nitrogen replacement: removing the residual liquid phase benzene in the micropores of the catalyst;

(5) nitrogen replacement: the nitrogen replacement step is only required if the superheated steam replacement is selected in the previous step;

(6) and (3) cooling: and (5) blowing air to reduce the temperature to below 40 ℃.

Patent CN 110721645 a discloses an environmental-friendly purging device and method for an ethylbenzene reactor. The patent uses heated nitrogen as a purging medium for removing benzene vapor remained in a catalyst bed layer, and also utilizes purified air to oxidize ferrous sulfide in a reactor to prevent the ferrous sulfide from spontaneous combustion. In order to solve the problem of environmental pollution, the sweeping tail gas is discharged to the atmosphere after being adsorbed by the activated carbon tower. The method is suitable for the purging operation of the catalyst in a dry gas ethylbenzene alkylation reactor without liquid phase benzene, if the method is used for a liquid phase ethylbenzene reactor, the large amount of liquid phase benzene retained in the catalyst can enable the activated carbon in an activated carbon tower to exceed the adsorption capacity, further the concentration of benzene in the exhaust tail gas exceeds the specified environment-friendly emission index (4ppm vol), and if the problem is solved by increasing the filling amount of the activated carbon, the method is not feasible economically. In addition, a condensation cooler is not arranged in front of the active carbon tower, and high-temperature tail gas enters the active carbon tower, so that the adsorption capacity of the active carbon is weakened.

Patent CN 209778701U discloses an ethylbenzene unit catalyst treatment unit in a styrene plant. The patent uses steam to heat nitrogen, uses hot nitrogen to once-through purge a liquid phase ethylbenzene catalyst bed layer to remove liquid phase hydrocarbon (benzene) and gas phase hydrocarbon (benzene), and discharges the hydrocarbon to a torch for incineration. The method has large nitrogen consumption, and the nitrogen carries all the liquid-phase benzene contained in the catalyst to a torch for incineration, thereby not only causing waste, but also bringing environmental pollution.

As can be seen from the related disclosure in the prior art, the established liquid phase ethylbenzene plant mainly adopts the following three methods to remove the liquid phase benzene retained in the catalyst: firstly, removing liquid-phase benzene and gas-phase benzene in an alkylation catalyst and a transalkylation catalyst by using a superheated steam sweeping method, and then sweeping water vapor remained in the alkylation catalyst and the transalkylation catalyst by using hot nitrogen; secondly, removing liquid-phase benzene and gas-phase benzene in the alkylation catalyst and the transalkylation catalyst by adopting circulating hot nitrogen; and thirdly, replacing the former two methods by adopting a mode of a large amount of hot nitrogen one-way purging. A brief liquid phase ethylbenzene reaction, separation system and first and third purge schemes are shown in FIG. 1.

The first method has low construction cost, can realize the purpose by only adding a nitrogen heater, but can cause the problem that steam condensate damages the aluminum skeleton of the catalyst and the problem of acid catalyst alkali poisoning; the second method has larger investment and occupied area of a circulating hot nitrogen system; the third method wastes a large amount of nitrogen and increases the VOC emission of benzene, a highly toxic substance. Therefore, it is necessary to find a more economical, scientific and environmental-friendly method to solve the problems in the prior art.

Disclosure of Invention

The invention aims to solve the defects in the prior art, provides a method for removing liquid-phase benzene retained in a catalyst of a liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging, has high removal efficiency, is beneficial to prolonging the service life of an ethylbenzene unit catalyst, and prevents the selectivity and the conversion rate of a regenerant from deteriorating.

The technical scheme of the invention is as follows: a method for removing liquid-phase benzene retained in a catalyst of a liquid-phase ethylbenzene alkylation and transalkylation reactor by superheated benzene vapor purging comprises the following specific processes:

1) sending liquid-phase benzene separated by a reaction product separation system in a liquid-phase ethylbenzene production device into a benzene vaporizer to be vaporized into benzene vapor;

2) the benzene vapor forms superheated benzene vapor after passing through a benzene superheater and is sent into an alkylation reactor or a trans-alkylation reactor;

3) superheated benzene vapor purges liquid-phase benzene retained in an alkylation or transalkylation catalyst bed layer to be gasified, and the gasified gas-phase benzene enters a reaction product separation system to be condensed into liquid-phase benzene;

4) after liquid-phase benzene retained in the alkylation or transalkylation catalyst bed is removed, the benzene vapor feeding of the benzene superheater is switched to nitrogen, and the nitrogen is heated by the benzene superheater and then sweeps the gas-phase benzene retained in the alkylation or transalkylation catalyst bed.

Further, the temperature of the superheated benzene steam for purging is 220-300 ℃.

Further, the steam pressure of the superheated benzene for purging is 0.01-1.0 MPaG.

Further, the space velocity of the superheated benzene vapor for purging is 2.01-60 h^-1。

The invention has the beneficial effects that:

1. the method uses superheated benzene vapor to purge the catalyst for alkylation and transalkylation of ethylbenzene by a liquid phase method, can successfully remove the liquid phase benzene in the catalyst, is more economic and environment-friendly, and creates conditions for safely entering a catalyst bed layer for maintenance or discharging the catalyst;

2. the method uses the superheated benzene vapor to replace superheated steam or nitrogen to purge the catalyst, and solves the problems that the superheated steam generates liquid water after evaporating liquid-phase benzene of the catalyst bed and condensing the superheated steam per se, and the liquid water damages the catalyst aluminum framework; the problem of overlarge investment of a circulating hot nitrogen system is also solved; the problems of overlarge nitrogen consumption and overlarge VOC discharge amount in one-way hot nitrogen purging are also solved;

3. the method disclosed by the invention strictly controls the temperature and pressure change speed of the benzene superheated steam, and can prevent the pressure drop of a catalyst bed layer from being increased or the catalyst from being lost to a separation process caused by crushing catalyst particles;

4. the system also uses a start-up heater and a nitrogen heater which are necessary for the liquid-phase ethylbenzene device as a benzene vaporizer and a benzene vapor superheater respectively to obtain superheated gas-phase benzene for purging and removing, and the construction cost of a production line is not increased;

5. the invention utilizes the prior ethylbenzene separation system in the device to condense and recover the removed benzene, has low equipment cost and investment and high construction benefit.

Drawings

FIG. 1 is a schematic flow diagram of a liquid phase ethylbenzene reaction, separation system and two purge processes;

FIG. 2 is a flow diagram of superheated benzene vapor purging to remove liquid phase benzene trapped in the catalyst;

FIG. 3 is a flow chart of the process of removing the liquid phase benzene retained in the catalyst by the superheated benzene vapor purging and removing device and recovering the benzene.

Wherein, 01: a benzene vaporizer; 02: a benzene superheater; 03: an alkylation reactor or a transalkylation reactor; 04: a reaction product separation system;

101: liquid phase benzene; 102: benzene vapor; 103: superheated benzene vapor; 104: gas-phase benzene obtained after liquid-phase benzene in the catalyst is evaporated; 105: nitrogen gas; purging the tail gas 106; 107 liquid phase benzene in the reactor bed blown off by superheated benzene vapour.

Detailed Description

The following examples further illustrate the present invention but are not to be construed as limiting the invention. Modifications and substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit of the invention.

Firstly, liquid-phase benzene 101 separated from a reaction product separation system 04 in a liquid-phase method ethylbenzene production device is sent to a benzene vaporizer 01, the liquid-phase benzene 101 is gasified into benzene vapor 102 by a heating heat source, then the benzene vapor is superheated by a benzene superheater 02, the superheated benzene vapor 103 is sent to an alkylation reactor or a trans-alkylation reactor 03, the liquid-phase benzene retained in an alkylation and/or trans-alkylation catalyst bed is vaporized by utilizing the sensible heat of the superheated benzene vapor, then the gas-phase benzene 104 evaporated along with the liquid-phase benzene in the catalyst enters the reaction product separation system 04 to be condensed into liquid-phase benzene, a part of the condensed liquid-phase benzene is used as the liquid-phase benzene 101 fed into the benzene vaporizer 01, and the liquid-phase benzene 107 in the reactor bed blown off by the superheated benzene vapor can be continuously used as an alkylation reaction raw material after being sent out.

After the liquid phase benzene retained in the alkylation or transalkylation catalyst bed is completely removed, the benzene vapor feeding of the benzene superheater 02 is switched to nitrogen 105, and the nitrogen is heated by the benzene superheater 02 and then sweeps the gas phase benzene retained in the alkylation or transalkylation catalyst bed.

At the beginning of nitrogen replacement, a part of gas-phase benzene carried by nitrogen to the reaction product separation system 04 is condensed into liquid-phase benzene, and gas-liquid separation is carried out; in the latter stage of the nitrogen displacement, as the concentration of benzene in nitrogen decreases, no liquid phase benzene condenses in the reaction product separation system 04. The stream of the purge tail gas 106 contains all the displaced nitrogen and benzene which is not condensed in the separation system, the purge tail gas is sent into a VOC treatment system or a steam superheater system for incineration, the benzene content in the analyzed tail gas is less than 4ppm, and the nitrogen displacement is qualified.

Compared with the existing liquid phase method ethylbenzene production process flow, the benzene vaporizer 01 used in the embodiment can be used as a start-up heater in the existing liquid phase method ethylbenzene process device, and the benzene superheater 02 can be used as an existing nitrogen heater, so that additional equipment is not needed.

On the basis of a 27-million-ton/year liquid phase method ethylbenzene device in operation, under the guidance of Changzhou Rehua chemical engineering technology GmbH, the operation method for the superheated benzene vapor purging alkylation catalyst bed layer to retain liquid phase benzene is realized by adding two pipelines.

The added lines are as follows:

(1) a pipeline is connected behind a reflux regulating valve of the light component tower, and DN50 and PN10 carbon steel pipelines are led out behind an outlet valve of a hydrocarbon circulating pump P-202 and are used for introducing liquid phase benzene to a start-up heater E-102;

(2) leading out from an interlocking cut-off valve at the inlet of the alkylation reactor and a field valve behind the interlocking cut-off valve, connecting to a blind plate at a tube pass steam pipeline boundary area of a nitrogen heater E-107, and configuring DN150 and PN2.5 carbon steel pipelines. The method is used for introducing gas-phase benzene gasified in a benzene heater, superheating the gas-phase benzene in a nitrogen heater, and purging liquid-phase benzene in a catalyst bed layer of a reactor by the superheated benzene according to the original steam purging process.

By providing the above two lines, the superheated benzene vapor purge scheme of FIG. 2 was established. And this work was carried out under the following operating conditions:

1. and in the process of purging the catalyst bed layer by the superheated benzene steam, the pressure control value in the purged reactor is 300 KPaG.

2. In the process of purging and heating the hot benzene vapor, the temperature difference between adjacent temperature measuring points of each bed layer of the reactor is not allowed to exceed 30 ℃ so as to prevent the liquid-phase benzene from overflowing from a catalyst pore passage too fast in the gasification process and crack and break the catalyst;

3. the flow of the liquid phase benzene is not allowed to exceed 8t/h because of the limitation of the flow provided by the reflux pump of the light component tower and the heat load of the aftercooler E-204 of the light component tower, and the control of the reflux flow regulating loop of the light component tower is taken as the standard.

4. At 300KPaG, the saturated vapor phase temperature of benzene is 130 deg.C, so when the temperature at the outlet of the start-up heater E-102 is below 130 deg.C, which means that liquid phase benzene may be carried into the nitrogen heater E-107, the benzene feed rate should be reduced.

5. The outlet temperature of the nitrogen heater E-107 was controlled between 220 ℃ and 240 ℃ by an outlet temperature controller. Under the condition of 300KPaG, the temperature of the purged reactor exceeds 160 ℃, and the liquid level of a reflux tank of the light component tower does not rise (under the condition of no discharge) and is kept qualified for 4 hours.

6. In the nitrogen replacement stage, the replaced tail gas containing benzene and nitrogen is sent to an operating ethylbenzene dehydrogenation unit, the tail gas containing benzene is sent to a tail gas absorption tower T-302 to recover benzene in nitrogen, and then the benzene and the tail gas are sent to an ethylbenzene dehydrogenation unit steam superheater F-301 to be burnt as fuel.

All 8 alkylation reactor beds were treated according to the example schemes, operating parameters and methods described above. The superheated benzene steam purging period lasts 17.6 hours in total, the hot nitrogen purging period lasts 9.3 hours in total, and the superheated benzene steam purging space velocity is 31 hours^-1. After natural cooling, the two bed catalysts at the bottom are discharged and sent to a professional catalyst manufacturer for regeneration. The specific surface area of the regenerated EBZ-500R alkylation catalyst is detected to be 482m²The specific surface area of a fresh EBZ-500R alkylation catalyst is 493m by comparison detection²The comparative area of the regenerant was only reduced by 2.23% per gram. Completely meets the requirements of catalyst suppliers UOP.

After the regenerant is returned to the reactor and the reactor is started, the ethylene conversion rate at the outlet of the regenerant bed layer is detected to be 100 wt%, the ethylbenzene selectivity is detected to be 95 mol%, and the difference is avoided compared with the working condition of a fresh EBZ-500R catalyst.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. However, the above description is only an example of the present invention, the technical features of the present invention are not limited thereto, and any other embodiments that can be obtained by those skilled in the art without departing from the technical solution of the present invention should be covered by the claims of the present invention.